High frequency coil assembly



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UNITED STATES PATENT OFFICE HIGH FREQUENCY COIL ASSEMBLY Redford K. Frazier, Chicago, 111., trainer to Bendix Radio Corporation Application June 2, 1938, Serial No. 211,361

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This invention relates to a high frequency coil assembly, and deals with a coil assembly particularly adapted for use in radio circuits.

An object of the invention is to provide an inductor suitable for use in connection with high frequencies and which has a very high reactance as compared with its resistance. It is also desired to provide an inductor which will have high reactance as compared with its resistance even when used within a magnetic shield.

Another object of the invention is to provide an assembly in which two inductors are magnetically coupled, and which, though magnetically shielded, may be easily adjusted from the exterior of the shielding to vary the coupling between the object of this invention to provide a coil which will have a very high Q at high frequencies, even though the coil be disposed within a magnetic shield.

In high frequency radio work it is common practice to use coils of cylindrical form which may have either an air core or an iron core of finely divided comminuted iron particles. The use of cores made of comminuted iron particles is generally considered superior because of the increased magnetic permeability. However, there has been no known way to construct iron core inductors which have very high Q ratings. It has been possible to construct air core coils of a very high Q value. For example, a cylindrical air core coil of about 3 inches in diameter and 4 inches in length may be constructed which has a Q as high as 400, but coils of such size are too large and cumbersome to be suitable for radio use. Also it has been found that magnetic shielding of radio frequency inductors of known types tends to materially reduce their Q rating. Accordingly, it is an important object of this invention to provide an iron core inductor which is compact in form and which has a very high Q rating. It is also desired that the Q of the coil be diminished by a minimum when the inductor is magnetically shielded.

I have found that by making the coil of the inductor in the form of a conoid or ellipsoid and mounting this coil on the end portion of a magnetic core, a structure is produced which will yield a very high Q rating, and that this structure may be magnetically shielded with but a small decrease in the Q rating of the device.

The improved coil end assembly will be more clearly understood with reference to the accompanying drawing in which- Figure 1 is an elevational view partly in section of a structure embodying the invention, the casing being broken away to show the interior structure;

Figure 2 is a view similar to Figure l but in en elevation;

Figure 3 is a perspective view of a series of the structures shown in Figures 1 and 2, mounted on a radio chassis;

Figure 4 is a detailed view of one embodiment of the improved inductor, the view being taken partly in section;

Figure 5 is a view of a modified form of inductor embodying the features of this invention, and

Figure 6 is another view of a modified form of inductor assembly, this modification being in the form of a transformer.

As illustrated in Figures 1 to 4 of the accompanying drawing, A designates a frame; B, a primary coil mounted in the frame; C, a secondary coil mounted in the frame; D, condensers electrically associated with coils B and C; and E, a magnetic shield about the structure.

The frame A may be of any suitable type, and as here shown comprises the posts iii, of any suitable material, which extend between the endplates H and I2. These plates may be of any suitable insulation material. Between posts I0 and bottom plate 12 is a shield plate l3 which forms a part of the magnetic shield about the assembly. The screws I5 extending through end plates H and I2 secure these plates firmly to post [0.

On the front side of frame A is the screw member it which has its ends journalled in the front pair of posts It. On the rear side of frame A is the guide bar [1 which has its ends secured in the rear pair of posts l0. Carried by screw member i8 and the guide bar I1 is the coil carrier l8 which, as here shown, comprises a plate of insulating material of the general shape shown, having a slot is which engages the guide bar l1, and having the tapped piece 20 which engages the screw member I6. In the construc-' tion shown the piece 20 has a slot 20 and the tiny portions 20 and 20 may be squeezed together to form a tight frictional engagement with the screw member i6. Secured to one end portion of the screw member I8 is a knurled wheel 2| which may be operated to rotate the screw l6 for moving the carrier l8 axially of the screw.

Mounted on carrier plate 3 is the improved inductor, more clearly illustrated in Figure 4 of the drawing. As illustrated, the inductor comprises a magnetic core 30 preferably composed of finely divided iron particles and having a substantially cylindrical outer surface. At the rear end portion 3| of this inductor is an axial indentation 32 into which is secured a threaded mounting bar 33. The core 30 may be conveniently mounted to plate i 8 by having the bar 33 extended through an opening in this plate and a nut 34 turned on to the end of bar 33.

The coil 35 comprises a number of turns of wire and is in the form of a conoid. The smaller endof the coil is secured to the surface of the core 30, and the outer larger end of the coil extends beyond the end of this core. Preferably, the surface formed by the coil 35 makes an angle of substantially 30 with the axis of the coil. Other inclinations such as 20 or 45 may be used to secure good results, but I have found that an inclination of about 30 is preferable. The end portion 36 of the core 30 extends'through the opening in the smaller end of the coil to about the longitudinal center of the. coil. As will be observed from Figure 4, the coil 35 is spaced from and is out of contact with the extended end of the core.

In constructing the improved inductor, the wire, which may be cotton covered orotherwise insulated, is wound upon a conical mandrel. If desired, one or more strips of cotton tape 39 may be extended longitudinally of the coil for providing structural support. After the winding is formed, a'coating' of some dielectric binder such as Q-max is applied to the'tums and cotton strips for structurally securing the turns in place. The coil is then removed from the mandrel and the core 30 inserted into the opening in the small er end.

trically connected in parallel with the coil of inductor C.

The magnetic shield E comprises a metal can of rectangular shape which fits over the condensers D and frame A enclosing the magnetically coupled inductors. The shield E, however, may take any other suitable form. At its top are the two openings 40 which provide means for access for tuning the condensers D, and on the front side of this shield is a slot 4| through which the knurled wheel 2| extends.

The base plate l2 rests upon an insulated plate 42 and is secured by such as the bolt 43 to any suitable base frame or chassis such as 44 seen more clearly in Figure 3 of the drawing. The bottom edge of the shield can E is adapted to resiliently engage the plate l3 and to be removable therefrom when desired.

As seen more clearly in Figures 1 and 2, contacts 45, which extend through openings in frame pieces 42 and 44, may be electrically connected through opposite ends of the coil on inductor'C; and the contacts 46, which also extend through openings in frame members 42 and 44, may be electrically connected through the opposite ends of coil on inductor B. The structure above described provides a pair of inductively coupled cir- The core and coil may be dipped into the Q-max' or other dielectric binder and the turns of the coil thus firmly secured together and to the core. I have found that best results are obtained if only the end turn or perhaps two turns at the end of the coil 35 are in contact with the,

core. It is essential that the end portion of the core which is disposed within the coil be free from and not in contact with the inner surface of the coil. As shown in Figure 4, an airspace 38 extends between the turns of wire and the portion 36 of the core. This construction is believed to be important .in obtaining a very high Q value. I have foundthat very good results may be obtained by using a coil of 23 turns and formed of size No. 24 cotton covered wire, and with a core of about diameter and long, for frequenciesof'from 6 to 9 megacycles. However, other sizes of core and wire and other numbers of turns may be used. I

Mounted on the top frame plate II is a secondary inductor C which may be structurally the same as inductor B just described. Inductor C has its axis extending vertically and is disposed immediately over the inductor B. Thus it will be clear that the two inductors B and C are magnetically coupled.

In the illustrated construction, a pair of condensers D are mounted on the top side of plate ll. One of these condensers, D1, is electrically connected in parallel with the coil 35 of inductor B; and the other of these condensers, D2, is eleccuits which may be tuned to the same frequency. Any number of these structures may be used in the latter apparatus as may be desired; as shown in Figure 3, three of such units are shown mounted side by side on the same frame base.

To adjust the apparatus for closer or looser coupling between the inductors it is not necessary for the operator to remove the magnetic shield, but through simple manipulation of the knurled wheel 2! which is accessible from the exterior of the casing, he may adjust the icoils to such position as to yield the desired coupling between the circuits. Turning of the knurled wheel causes screw member I6 to rotate and this produces axial. movement of the inductor B which changes the Just described, yield a much higher Q value. I

found that with coils of the ordinary type in which a number of turns are wound in contact with a cylindrical core, the Q value obtained in one instance was 180, while with the improved inductor of this invention the Q value obtained was 240. In the same situation I found that when an inductor having its winding in the form of a 45 conoid was used, the Q rating was 210. Also I found that the addition of a metallic shield reduced the Q of the ordinary coil from 180 to 130, while in the case of the improved inductor the Q was reduced from 240 to 215. Thus it is clear that the improved inductor is not only more efficient but is less aifected by the presence of a metallic shield. The quantities mentioned in the above example are illustrativeonly and are given only for the purpose of indicating the advantage to be gained by the inductor of improved construction.

In Figure 5 is shown a modified, form of inductor which is identical with the type shown in Figure 4 except that the winding 46 determines,

substantially the surface of an ellipsoid rather than a conoid. As here shown the winding 46 flares outwardly from ts smaller end and is entirely free from the e tended core end 41. This in making them structurally secure. This modi-.

fled type of inductor may be mounted Just as was described in the case of inductor B and may be substituted for inductorB whenever desired.

' Another modified construction is shown in Figure 6. This modification comprises a core W in the form of a bar which may be cylindrical in shape. About one end portion of the bar extends a primary coil Ii which is a coil similar to coil 38 already described. Coil II has its smaller end secured to the exterior of core 50 and determines a surface which makes an; angle of about 30 with the axis of. the core. 'As in the case of the first described embodiment, the core 80 extends into the interior of coil Bl to about the longitudinal center of the coil. Extending about the other end of core 50 is the coil 52 which has its smaller end secured to this core, and which determines a surface mak- 30 with its axis, said coil being disposed coing an angle of about 30 with the axis of the core 50. The construction of this embodiment may be generally the same as already described in the first mentioned embodiment. Preferably the core 50 is of finely divided magnetic materials firmly bound together in a way already known to the art. The structure shown in Figure 6 may be used as a high frequency transformer, one of the coils Bi and 52 being the primary winding, and the other of these coils being the secondary winding. The same advantages as to high Q quality is here obtained as in the case of the preferred embodiment.

It is apparent that many other embodiments may be constructed, and many changes may be made in the details of construction without departing from the spirit of the invention. The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations should be understood therefrom but the appended claims should be construed as broadly as permissible in view of the prior art.

What I claim is:

1. Anelectrical inductor comprising a coil having a plurality of turns and determining an outwardly flaring surface toward its larger end, said coil having openings at each of its ends, and a magnetic core of .finely divided comminuted magnetic material disposed within the opening at the smaller end of said coil and extending axially within said coil to a terminus substantially mid way between said ends, the extended end of said, core being spaced from and out of contact with said coil. v

2. An electrical inductor comprising a magnetic core of finely divided, materials and cylindricai in form, and-a coil of wire comprising a plurality of turns and determining a conical surface which makes an angle of substantially axially with said core and having one of its turns at its smaller end secured to the surface of said cylindrical core, and the larger end of said coil extending axially beyond one end of said core 'with the coil being spaced from the said end of the core.

3. An electrical transformer comprising a magnetic'core of finely divided materials and in the form of a bar, a primary coil having a plurality of turns and determining an outwardly flaring surface towards its larger end, said coil extending about one end portion of said core and having its larger end extending axially beyond and free from said end of the core, and a secondary coil comprising a plurality of turns and determining an outwardly flaring surface towards its larger end, said secondary coil'extending axially beyond and free from the extreme end of the other end portion of said core.

4. An electrical inductor comprising a coil having a plurality of turns and determining a surface substantially in the form of an ellipsoid, said coil having a smaller end opening and a larger end opening, and a magnetic core extending through said smaller end opening and termi ting within the interior of said coil, said coil being spaced and free from the interior end of said core.

5. An electrical inductor comprising a coil having a plurality of turns of insulated wire and determining a fiaring surface substantially in the form of anellipsoid and having a small end coil having openings at each of said ends, and a magnetic core supporting said coil and extending through the opening of the smaller of said end portions and terminating within said coil at a point intermediate said end portions.

'I. An electrical inductor comprising a coilhaving end portions of different diameters, said coil having openings at each of said ends, and a cylindrical magnetic core supporting said coil and extending through the opening of the smaller of said end portions and terminating within said coil at a point intermediate said end pertions, the major portion of said core beingdisposed outside thelimits of said coil. 7

RADFORD K. 

